The present invention relates to a color graphic image processing system, more particularly, to a novel image processing system for processing color graphic image.
Japanese Patent Laid-Open No. 161982/1984 represents a system for processing full-color image, i.e., normal color image.
Such a system first reads a full-color image to be processed as 8-bits input signals, then compensates for shading, i.e., compensating for unevenness of optical luminance, and then executes gamma compensation. Gamma compensation allows the output copy density corresponding to the input original density to be output as 6-bits signals by the degrading characteristic of the dither cumulative frequency in conjunction with the voltage output from charge-coupled device (CCD) in order that the relationship between these density values can remain 1:1 independent of uneven characteristics of input and output systems. The system presented by the above prior art then properly adjusts tonal characteristics of respective chrominance signals in accordance with masking compensation and UCR compensation processes. The system then converts half-tone image into binary codes using a dither processing circuit, and then it executes pulse width modulation using a multilevel conversion circuit to improve tonal characteristic of the half-tone image before eventually allowing a laser printer to reproduce a picture virtually identical to the image to be processed.
Japanese Patent Laid-Open No. 57573/1984 proposes a technique for sharpening a picture image by converting signals received from other than white level close to white area into signals indicating white color. This operation taking place before encoding of the signals into binary codes takes place and simultaneously with the conversion of signals other than black level close to black area into signals indicating black color.
The system in Japanese Patent Laid-Open No. 161982/1984 aims at processing a full-color image. The system applies 8-bits data to each of three primary colors comprised of red, green, and blue components, which allows each picture element to be represented by about 16 million colors. This system executes all the needed processing operations by reading image signals of full-color consisting of normal colors, thus obliging each picture element to represent color images by applying 24-bits (8-bits.times.3). Since many conventional personal computers and microprocessors available today process with 8-bits data width, the system proposed by the Japanese Patent Laid-Open No. 161982/1984 cannot easily be operated with many conventional personal computers and microprocessors presently available. Furthermore, the system of Japanese Patent Laid-Open No. 161982/1984 aims at precisely reproducing pictures by reading the original image signals. To achieve this aim, this system executes a variety of processes including shading compensation, gamma compensation, masking process, UCR process, dither process, and conversion of read image signals into binary codes, and as a result, this system unavoidably needs to execute complex data processing operations using a complicated system constitution.
The image processing device proposed by Japanese Patent Laid-Open No. 57573/1984 first detects edges of the original picture by applying an edge-detection operator such as Laplacean operator or a differential operator before eventually sharpening edges of images by modifying the density value of picture elements in the periphery of picture edges. As a result, if characters or lines having extremely thin configuration are present, the system related to the above art cannot easily detect the substance of fine characters or lines, and in addition, since it is difficult for this system to correctly determine the density value of fine characters or lines, it cannot easily determine the modified density value of picture elements in the periphery of picture edges, thus resulting in the difficulty for the system to securely reporduce edges having sharper contrast effect.
The inventors of the present invention expanded upon studies done on color graphs, which are substantially artificial images, and eventually discovered a variety of characteristics enumerated below. Noting that each full image is composed of a variety of colored images observing such a variety of images from a clearly visible distance, a color graph represents a specific colored area in which gradual color variation is not present.
(1) A picture generally contains ten or so colors in all.
(2) Colors appearing in respective areas which are uniform can represent certain values of information.
(3) A color graphic picture contains both colored characters and fine lines.
Accordingly, if a specific process identical to that which is applicable to a full-color picture is also applied to color graph, a variety of problems take place such as those described below.
(1) Any conventional color scanner made available for an input device provides 256 units of tone wedge per each component of three primary colors, while 24 bits (8-bits.times.3) of data are needed for each picture element. In addition, each color scanner must be provided with practically workable linearity throughout 256 tone wedges, thus an expensive system.
(2) Although the color scanner needs a complex constitution, optical characteristics of each color scanner like spectro-sensitivity distribution for example, and physical characteristics like aperture size such as that obtained in utilizing an iris diaphragm for example, are different from each other. Actually, image signals received from various input devices do not always match certain colors. Note that spectro-sensitivity distribution is the distribution of output signals against light having a specific frequency.
(3) When converting an image presented in a specific area where the image color is visually uniform into a signal using a color scanner, the image-converted signal doesn't show a constant value. In addition, even if there is such a specific area where color graph visually remains in uniform color effect, after delivering color via an output unit, it may eventually be determined that uneven color effect is still present in this area.
(4) Extraction of characters and fine lines from a specific area involves a certain difficulty. More particularly, since the dynamic range which is substantially the object of quantization is relatively wide, the image signal from any conventional color scanner doesn't show a constant value in a specific portion which is visually seen uniform by human eyes. Consequently, if the portion visually seen uniform by human eyes should be extracted, it is necessary for the operator to implement any processing operation such as smoothing process for converting fine structure into a widely visible range for example in order that the density value can be stabilized in the needed portion by means of compensation. However, if a smoothing process is applied, fine configuration of characters and fine lines cannot properly be held unaffected. To compensate for this, it is necessary for the color graphic processing system to preliminarily apply a masking process to finely composed characters and fine lines, which in turn results in a requirement for complicated processes to be carried out.
(5) A data input unit is generally provided with a capacity for producing 8-bits and 256 tone-wedge color data signals in conjunction with each component of three primary colors. On the other hand, a data output unit is generally provided with such a low capacity for delivering outputted data that a maximum of 4-bits color data signals per each component of three primary colors is realized. Normally, a data output unit is allowed to output about 1-bit color data signals. As a result, although the data input unit can produce 16 million colors expressed by 8-bits data per picture element, the data output unit can merely output 8 colors expressed by 1-bit data per picture element. This unavoidably generates a significantly large gap in the amount of information between the chromatic resolution of the data input and the chromatic expression capacity of the data output unit.